sometimes 1 or more engines in a stage will fail to ignite, if this happens once it will happen everytime the same rocket is lanched, when clicked on the unignited engines will say they have been actived but produce no thrust or effects whatsoever, i can't find any way of reproducing this bug it appears to happen at random, sometimes this bug will appear on rockets that worked previously after making minor adjustments and yes, i checked my staging.
@AndrewGarrison good to hear